Le Conte Glacier starts from the Stikine Icefield in the Coast Mountains of British Columbia, at an elevation of about 8,500 feet (2,591 m) between Devils Thumb and Mount Gilroy, and flows generally south for 22 miles (35 km) to Southeast Alaska at the head of Le Conte Bay in Frederick Sound, about 25 miles (40 km) north of Wrangell and 22 miles (35 km) east of Petersburg, Alaska. Le Conte Bay is a fjord over 1,000 feet (305 m) deep near the terminus of the glacier and is presently about 10 miles (16 km) long opening to the southeastern head of Frederick Sound adjacent to the Stikine River delta. Frederick Sound, a large fjord, separates Kupreanof Island to the south from Admiralty Island to the north and the islands of Kupreanof and Mitkof from the Southeast Alaska mainland. It was first charted in 1794 by Lieutenants Joseph Whidbey and James Johnstone and later named by Captain George Vancouver for Prince Frederick, Duke of York and Albany. Its head connects to Sumner Strait to the south via Dry Strait—a water passage generally not navigable by large vessels—which will eventually close as the advancing Stikine River delta progrades. In 1879, naturalist John Muir visited Le Conte Glacier when icebergs occupied a 10- to 12-mile (16- to 19‑km) stretch of the bay. In The American Geologist, he noted that the Tlingit called the fjord ‘Hulti,’ meaning ‘Thunder Bay,’ in reference to the noise generated by calving icebergs. In 1887, the US Coast and Geodetic Survey ship Carlile P. Patterson mapped the Southeast Alaska coast. Lieutenant Commander Charles M. Thomas subsequently named the glacier in honor of Joseph Le Conte, a close friend of Muir. From 1857 to 1869, Le Conte was a professor of chemistry and geology at South Carolina College (now the University of South Carolina). In 1869, he moved to Berkeley, California, to become a professor of geology at the newly established University of California. Renowned for his exploration and preservation of California’s Sierra Nevada, he first visited Yosemite Valley in 1870, where he befriended Muir and began exploring the Sierra. In 1892, Le Conte co-founded the Sierra Club with Muir and others and served as its director until 1898.

Le Conte Glacier is a tidewater glacier—an ice stream that terminates in the ocean at either a grounded terminus or a floating ice tongue. Glaciologists describe a recurring cycle for tidewater glaciers. Over centuries, they slowly advance until thinning near the terminus triggers a rapid retreat that concludes within decades; stability is reached only when the glacier retreats into shallow water. Although climatic changes may trigger the retreat, observations indicate that, once initiated, glacier behavior is only weakly influenced by climate; geometry plays a more important role. The ability of tidewater glaciers to discharge large volumes of ice quickly poses hazards to shipping and may contribute significantly to sea level rise. The Coast Mountains, which straddle the boundary between Alaska and British Columbia, currently have four tidewater glaciers—Sawyer, South Sawyer, Dawes, and Le Conte—covering a total area of 443,800 acres (179,600 ha). These glaciers are all thinning and retreating, though none are rapidly retreating. Le Conte Glacier, the southernmost tidewater glacier in the Northern Hemisphere, has attracted considerable study for its short-term ice calving dynamics and glacier–ocean interactions. It covers 115,892 acres (46,900 ha) and has an accumulation area at elevations between 3,020 and 8,530 feet (920-2,600 m). Between 1887 and 1963 the glacier retreated 2.5 miles (4 km), calving icebergs up to 980 feet (300 m) thick, before remaining relatively stable for 32 years. In 1994 it entered a phase of rapid retreat, and the terminus has since retracted about 1.2 miles (2 km). By 1998 the glacier had entered a phase of temporary stability at a constriction in the fjord—a pinning point that occurs when a narrowing or shoaling fjord reduces calving and the accumulation area equals the ablation area. This process is currently occurring with Le Conte Glacier, which—at its retracted position—appears likely to advance once a terminus shoal forms.

Although climate is the primary factor influencing glacier behavior, additional factors affect iceberg calving in tidewater glaciers. Climate change shifts the elevation of a glacier’s equilibrium line—the boundary above which snowfall accumulates faster than it melts and below which the reverse occurs. An upward shift triggers retreat, while a downward shift advances the terminus. However, the behavior of calving glaciers also depends on fjord geometry. Unlike land‐terminating glaciers, which decelerate near the terminus, tidewater glaciers accelerate as they approach the ocean. The rate of ice calving depends largely on glacier velocity and the water depth at the terminus. Glacier retreat in Alaska has contributed disproportionately to global sea-level rise, with these glaciers losing 75 billion tons of ice annually. Over the past 50 years, retreating glaciers and ice caps worldwide have contributed 0.02 inches (0.5 mm) per year to sea-level rise. Although mountain glaciers hold less than 1 percent of Earth’s glacial ice, their rapid shrinkage accounts for nearly 30 percent of current sea-level rise. Climate-induced melting is the primary cause of mountain glacier loss and will remain a major driver of global sea-level change. Sea-level rise is driven chiefly by the thermal expansion of seawater and by the transfer of water from terrestrial reservoirs—including land ice and groundwater—to the ocean. The Intergovernmental Panel on Climate Change Fourth Assessment Report found that thermal expansion accounted for about 25 percent of the observed sea-level rise from 1961 to 2003, while melting land ice contributed less than 50 percent and changes in land water storage less than 10 percent. During the final decade of that period (1993–2003), thermal expansion and land ice melt each contributed about 50 percent to sea-level rise. In the latest estimate for 1993–2008, land ice melt contributed 68 percent, while thermal expansion accounted for 35 percent. Read more here and here. Explore more of Le Conte Glacier and Frederick Sound here: